Stratospheric Welsbach seeding for reduction of global warming

ABSTRACT

A method is described for reducing atmospheric or global warming resulting from the presence of heat-trapping gases in the atmosphere, i.e., from the greenhouse effect. Such gases are relatively transparent to sunshine, but absorb strongly the long-wavelength infrared radiation released by the earth. The method incudes the step of seeding the layer of heat-trapping gases in the atmosphere with particles of materials characterized by wavelength-dependent emissivity. Such materials include Welsbach materials and the oxides of metals which have high emissivity (and thus low reflectivities) in the visible and 8-12 micron infrared wavelength regions.

BACKGROUND OF THE INVENTION

This invention relates to a method for the reduction of global warmingresulting from the greenhouse effect, and in particular to a methodwhich involves the seeding of the earth's stratosphere withWelsbach-like materials.

Global warming has been a great concern of many environmentalscientists. Scientists believe that the greenhouse effect is responsiblefor global warming. Greatly increased amounts of heat-trapping gaseshave been generated since the Industrial Revolution. These gases, suchas CO₂, CFC, and methane, accumulate in the atmosphere and allowsunlight to stream in freely but block heat from escaping (greenhouseeffect). These gases are relatively transparent to sunshine but absorbstrongly the long-wavelength infrared radiation released by the earth.

Most current approaches to reduce global warming are to restrict therelease of various greenhouse gases, such as CO₂, CFC, and methane.These imply the need to establish new regulations and the need tomonitor various gases and to enforce the regulations.

One proposed solution to the problem of global warming involves theseeding of the atmosphere with metallic particles. One techniqueproposed to seed the metallic particles was to add the tiny particles tothe fuel of jet airliners, so that the particles would be emitted fromthe jet engine exhaust while the airliner was at its cruising altitude.While this method would increase the reflection of visible lightincident from space, the metallic particles would trap the longwavelength blackbody radiation released from the earth. This couldresult in net increase in global warming.

It is therefore an object of the present invention to provide a methodfor reduction of global warming due to the greenhouse effect whichpermits heat to escape through the atmosphere.

SUMMARY OF THE INVENTION

A method is disclosed for reducing atmospheric warming due to thegreenhouse effect resulting from a greenhouse gases layer. The methodcomprises the step of seeding the greenhouse gas layer with a quantityof tiny particles of materials characterized by wavelength-dependentemissivity or reflectivity, in that said materials have highemissivities in the visible and far infrared wavelength regions and lowemissivity in the near infrared wavelength region. Such materials caninclude the class of materials known as Welsbach materials. The oxidesof metal, e.g., aluminum oxide, are also suitable for the purpose. Thegreenhouse gases layer typically extends between about seven andthirteen kilometers above the earth's surface. The seeding of thestratosphere occurs within this layer. The particles suspended in thestratosphere as a result of the seeding provide a mechanism forconverting the blackbody radiation emitted by the earth at near infraredwavelengths into radiation in the visible and far infrared wavelength sothat this heat energy may be reradiated out into space, thereby reducingthe global warming due to the greenhouse effect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome more apparent from the following detailed description of anexemplary embodiment thereof, as illustrated in the accompanyingdrawings, in which:

FIG. 1 illustrates a model for the heat trapping phenomenon, i.e., thegreenhouse effect.

FIG. 2 is a graph illustrating the intensity of sunlight incident onearth and of the earth's blackbody radiation as a function ofwavelength.

FIG. 3 is a graph illustrating an ideal emissivity versus wavelengthfunction for the desired particle material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a model for the heat-trapping (greenhouse effect)phenomenon. It is assumed that the greenhouse gases are concentrated ataltitudes between y=0 (at some altitude Y₁, above the earth's surface)and y=1. Regardless of the sunshine reflected back into space, i₁ and i₂denote the shortwavelength sunlight energies that are absorbed by theearth's surface and the greenhouse gases, respectively. Available datashows that i₁ =0.45 i_(sol) and i₂ =0.25 i_(sol), where i_(sol) is thetotal flux from the sun. The short wavelength sunlight heats up thegreenhouse gases and the earth surface, and this energy is eventuallyreradiated out in the long wavelength infrared region.

FIG. 2 is a graph illustrating the intensity of sunlight and the earth'sblackbody radiation as a function of wavelength. As illustrated, some30% of the sunlight energy is in the near infrared region. The earth'sblackbody radiation, on the other hand, is at the far infraredwavelength.

Referring again to FIG. 1, I_(s), I₊, I₋, I_(g) and I_(e) represent thefluxes in the infrared wavelength region, where I_(s) and I_(g) are thefluxes reradiated by the greenhouse gases toward the sky and ground,respectively; I_(e) is the flux reradiated by the earth; and I₊ and I₋are fluxes within the gases radiating toward the space and ground,respectively. I₊ and I₋ are functions of y, e.g., I₊ (0) is the I₊ fluxat y=0. Considering the principles of energy conservation and continuityat boundaries, the following relationships are obtained:

    I.sub.s =i.sub.1 +i.sub.2                                  (1)

    I.sub.s =I.sub.+ (1)(1-R.sub.l)                            (2)

    I.sub.- (1)=I.sub.+ (1)R.sub.l                             (3)

    I.sub.+ (0)=I.sub.- (0)R.sub.o +I.sub.e (1-R.sub.o)        (4)

    I.sub.g =I.sub.- (0)(1-R.sub.o)+I.sub.e R.sub.o            (5)

    I.sub.e =I.sub.BB (T.sub.e)(1-R)+I.sub.g R                 (6)

    I.sub.e =i.sub.1 +I.sub.g                                  (7)

where R_(o), R_(l) and R are the reflectivities at the y=0 and y=1boundaries and at the earth's surface. I_(BB) (T_(e)) is the blackbodyradiation flux at the earth's temperature T_(e). Within the greenhousegases' layer, the energy equations are

    (dI.sub.+ /dy)=I.sub.BB (T.sub.g)-αI.sub.+           (8)

    -(dI.sub.- /dy)=I.sub.BB (T.sub.g)-αI.sub.-          (9)

where I_(BB) (T_(g)) is the blackbody radiation flux at the greenhousegases' temperature T_(g), and α is the absorption coefficient of thegases. The solutions of equations 8 and 9 are given by equations 10 and11:

    I.sub.+ (y)=(I.sub.BB /α)+Ce.sup.αy            (10)

    I.sub.- (y)=(I.sub.BB /α)+De.sup.+αy           (11)

To illustrate the effects of R_(o) and R_(l) on the green-house effect,the extreme case is considered wherein a high concentration ofgreenhouse gases has strong absorption in the infrared region; that is,for y=1, e⁻αl approaches 0. Then, using Equations 3 and 4, therelationships of Equations 12 and 13 are obtained.

    C=(I.sub.e -(I.sub.BB /α))(1-R.sub.o)                (12)

    D=0

From Equations 5 and 7,

    I.sub.e =i.sub.1 +I.sub.- (0)(1-R.sub.o)+I.sub.e R.sub.o,

or

    I.sub.e =(i.sub.1 /(1-R.sub.o))+(I.sub.BB /α).       (14)

From Equations 2 and 1,

    I.sub.s =(I.sub.BB /α)(1-R.sub.l)=i.sub.1 +i.sub.2,

or

    (I.sub.BB /α)=(i.sub.1 +i.sub.2)/(1-R.sub.l).        (15)

Combining Equations 14 and 15, the relationship of Equation 16 isobtained.

    I.sub.e =i.sub.1 /(1-R.sub.o)+(i.sub.1 +i.sub.2)/(1-R.sub.l)(16)

Finally, Equation 6 gives the blackbody radiation from the earth'ssurface in terms of i₁ and i₂ and the three reflectivities:

    I.sub.e =I.sub.BB (T.sub.e)(1-R)+(I.sub.e -i.sub.1)R

    I.sub.BB (T.sub.e)=I.sub.e +(R/(1-R))i.sub.1

or

    I.sub.BB (T.sub.e)=i.sub.1 /(1-R.sub.o)+(i.sub.1 +i.sub.2)/(1-R.sub.l)+(R/(1-R))i.sub.1                    (17)

To achieve a lower temperature of the earth, (considering i₁, i₂ and Ras constants), it is desirable to make R and R_(l) as small as possible.

Known refractory materials have a thermal emissivity function which isstrongly wavelength dependent. For example, the materials may have highemissivity (and absorption) at the far infrared wavelengths, highemissivity in the visible wavelength range, and very low emissivity atintermediate wavelengths. If a material having those emissivitycharacteristics and a black body are exposed to IR energy of equalintensity, the selective thermal radiator will emit visible radiationwith higher efficiency (if radiation cooling predominates), i.e., theselective thermal radiator will appear brighter than the black body.This effect is known as the Welsbach effect and is extensively used incommercial gas lantern mantles.

Welsbach materials have the characteristic of wavelength-dependentemissivity (or reflectivity). For example, thorium oxide (ThO₂) has highemissivities in the visible and far IR regions but it has low emissivityin the near IR region. So, in accordance with the invention, the layerof greenhouse gases is seeded with Welsbach or Welsbach-like materialswhich have high emissivities (and thus low reflectivities) in thevisible and 8-12 micrometer infrared regions, which has the effect ofreducing R_(o) and R_(l) while introducing no effect in the visiblerange.

A desired material for the stratospheric seeding has a reflectioncoefficient close to unity for near IR radiation, and a reflectioncoefficient close to zero (or emissity close to unity) for far IRradiation. FIG. 3 is a graph illustrating an ideal emissivity versuswavelength function for the desired material. Another class of materialshaving the desired property includes the oxides of metals. For example,aluminum oxide (Al₂ O₃) is one metal oxide suitable for the purpose andwhich is relatively inexpensive.

It is presently believed that particle sizes in the ten to one hundredmicron range would be suitable for the seeding purposes. Largerparticles would tend to settle to the earth more quickly.

The particles in the required size range can be obtained withconventional methods of grinding and meshing.

It is believed that the number of particles n_(d) per unit area in theparticle layer should be defined by Equation 18:

    n.sub.d 1≧1/σ.sub.abs                         (18)

where 1 is the thickness of the particle layer and σ_(abs) is theabsorption coefficient of the particles at the long IR wavelengths. Onecrude estimate of the density of particles is given by Equation (19):

    n.sub.d 1≧(cmw)/(4πe.sup.2)                      (19)

where c is the speed of light, m is the average particle mass, e is theelectron charge, and w is the absorption line width in sec⁻¹.

The greenhouse gases are typically in the earth's stratosphere at analtitude of seven to thirteen kilometers. This suggests that theparticle seeding should be done at an altitude on the order of 10kilometers. The particles may be seeded by dispersal from seedingaircraft; one exemplary technique may be via the jet fuel as suggestedby prior work regarding the metallic particles. Once the tiny particleshave been dispersed into the atmosphere, the particles may remain insuspension for up to one year.

It is understood that the above-described embodiment is merelyillustrative of the possible specific embodiments which may representprinciples of the present invention. Other arrangements may readily bedevised in accordance with these principles by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A method of reducing atmospheric warming due tothe greenhouse effect resulting from a layer of gases in the atmospherewhich absorb strongly near infrared wavelength radiation, comprising thestep of dispersing tiny particles of a material within the gases' layer,the particle material characterized by wavelength-dependent emissivityor reflectivity, in that said material has high emissivities withrespect to radiation in the visible and far infrared wavelength spectra,and low emissivity in the near infrared wavelength spectrum, wherebysaid tiny particles provide a means for converting infrared heat energyinto far infrared radiation which is radiated into space.
 2. The methodof claim wherein said material comprises one or more of the oxides ofmetals.
 3. The method of claim 1 wherein said material comprisesaluminum oxide.
 4. The method of claim 1 wherein said material comprisesthorium oxide.
 5. The method of claim 1 wherein said particles aredispersed by seeding the stratosphere with a quantity of said particlesat altitudes in the range of seven to thirteen kilometers above theearth's surface.
 6. The method of claim 1 wherein the size of saidparticles is in the range of ten to one hundred microns.
 7. The methodof claim wherein said material comprises a refractory material.
 8. Themethod of claim 1 wherein said material is a Welsbach material.
 9. Themethod of claim 1 wherein the number of said dispersed particles perunit area in the particle layer is greater than or equal to 1/σ_(abs) 1,where 1 is the thickness of the particle layer and σ_(abs) is theabsorption coefficient of the particles at the far infrared wavelengths.10. A method for reducing atmospheric warming due to the greenhouseeffect resulting from a greenhouse gases layer, comprising the followingstep:seeding the greenhouse gases' layer with a quantity of tinyparticles of a material characterized by wavelength-dependent emissivityor reflectivity, in that said materials have high emissivities in thevisible and far infrared wavelength spectra and low emissivity in thenear infrared wavelength spectrum, whereby said particles are suspendedwithin said gases' layer and provide a means for converting radiativeenergy at near infrared wavelengths into radiation at the far infraredwavelengths, permitting some of the converted radiation to escape intospace.
 11. The method of claim 10 wherein said material comprises one ormore of the oxides of metals.
 12. The method of claim 10 wherein saidmaterial comprises aluminum oxide.
 13. The method of claim 10 whereinsaid material is thorium oxide.
 14. The method of claim 10 wherein saidseeding is performed at altitudes in the range of seven to thirteenkilometers above the earth's surface.
 15. The method of claim 10 whereinsaid material comprises a refractory material.
 16. The method of claim10 wherein said particle size is in range of ten to one hundred microns.17. The method of claim 10 wherein said material is a Welsbach material.18. The method of claim 10 wherein the number of said dispersedparticles per unit area in the particle layer is greater than or equalto 1/σ_(abs) 1, where 1 is the thickness of the particle layer andσ_(abs) is the absorption coefficient of the particles at the farinfrared wavelengths.